Production of nitrocellulose



United States Patent M PRODUCTION OF NITROCELLULOSE Ronald Arthur Furlong, West Kilbride, Scotland, assignor to Imperial Chemical Industries Limited, a corporation of Great Britain No Drawing. Application April 19, 1954 Serial No. 424,273

Claims priority, application Great Britain June 10, 1953 3 Claims. (Cl. 260-223) In one method of preparing nitrocellulose from woodpulp the procedure used is to subdivide the woodpulp sheet, which may be, for example one sixteenth of an inch thick, into small pieces, for example squares of side about one eighth of an inch whichare then treated with a nitrating acid composition containing not less than about 40% nitric acid. The method of nitration may be by the socal'led mechanical process in which a portion ofthe acid is placed in a vessel followed by the cellulose and the re mainder of the acid runin and the reaction continued with stirring until nitrationis judged to be complete. The acid may then be centrifuged oft" and the product drowned in an excess of water after which it is subjected to further treatment such as kiering or boiling to reduce its viscosity, followed by washing and removal of excess water. The so-called dense nitrocellulose so obtained is still in the physical form of the cellulose prior to nitration. In an attempt to convert this dense nitrocellulose into a product having the form and characteristics of a nitrocellulose prepared from cotton linters it has been proposed to cut the resulting dense nitrocellulose in a pulper at any stage after nitration. This is not entirely satisfactory, however, as this cutting does not give a completely fibrous product but rather one which contains hard pips or centres which require prolonged agitation to dissolve them in the normal solvents used for this purpose.

It has also been proposed to achieve the same object by disintegrating the so-called dense nitrocellulose obtained after the viscosity reduction or stabilisation stage. This method also is not satisfactory since the product at this stage is. extremely brittle and on disintegration gives a product containing a large proportion of fine material which is difficult to separate from the process efiluents and thus leads to unduly large process losses.

It has further been proposed to prepare nitrocellulose from woodpulp by processes involving the step by flufiing, shredding or disintegration of the woodpulp prior to nitration. These processes, however, yield a finely divided product from which process losses are high.

It has now been found that a product similar to that obtained by the nitration of cotton linters can be ob tained by milling nitrated cut woodpulp sheet prior to kiering or boiling in which the milling is carried out in a mill of the kind consisting of two opposing discs which rotate relatively to each other.

According to the present invention the process for the production from subdivided sulphite woodpulp sheet of nitrocellulose which dissolves rapidly in solvents therefor and which has the form of nitrated cotton linters comprises nitrating the pieces of woodpulp sheet, adding water to the resulting nitrocellulose which is in the form of nitrated pieces of woodpulp sheet to produce an aque- 2,822,352 Patented Feb. 4, 1958 ous slurry thereof, passing said slurry between two opposed surfaces rotating relatively to one another and so spaced from one another as to be capable of effecting the separation of the fibers of the nitrated pieces of woodpulp sheet without subdividing the said fibres to any substantial degree, and thereafter effecting viscosity reduction and stabilisation of the resulting separated fibres of nitrocellulose.

The said aqueous slurry of nitrated pieces of woodpulp sheet may be passed several times between said two opposed surfaces.

The two opposed surfaces which are rotatable relatively to one another and are capable of being spaced from one another to the desired distance are the opposed surfaces of plates of a mill and the slurry of nitrated pieces of woodpulp sheet can therefore be said to be milled when passed between said surfaces.

The steps in the process of the invention, other than the milling step, may be carried out as in any of the hitherto known processes for producing nitrocellulose from woodpulp. Thus the nitration may be carried out, for example, by the pot process, the displacement process, or by the mechanical process. Removal of acid may be eifected by, for example, displacement or centrifuging followed by drowning. Washing may also be effected in a similar manner and stabilisation may be by boiling or kiering. In some instances it may be desirable to subject the milled nitrocellulose to a pulping step in the same way as nitrocellulose prepared from cotton linters is pulped.

Normally in mills of the type used for the milling step in the process of the invention one plate is fixed and the other rotates while the material to be milled is fed in through the centre of the stationary plate and removed at a point on the periphery. Grooved plates in which the grooves are deep at the centre and decrease in depth to the periphery give highly satisfactory results and it is preferred in carrying out the process of the invention to use a mill having plates of this latter type. Mills of the kind found suitable for the carrying out of the process of the invention are described for example in Chemical Engineers Handbook, editor: J. H. Perry, 3rd edition, p. 1144, Fig. 48. v

The nitrated woodpulp is passed through the mill in the form of a slurry and although one passage is normally sufiicient several passages may be employed if desired. The nitrated product may be milled before, during or after the preliminary washing stage, but milling must take place prior to boiling or kiering. Very little fine material is produced by the process of the invention and it is almost entirely bound within loose bundles of nitrated fibre which are curled or loosely bailed by the rotary action of the mill.

The invention is illustrated by the following examples in which all parts and percentages are by weight.

Example 1 2,160 lb. of a sulphite woodpulp sheet are diced into pieces about one eighth inch square and treated with 21,600 lb. of a mixed acid containing 50.05% nitric acid, 37.88% sulphuric acid, 0.02% nitrous acid and 12.05% water for 2 hours. The nitrated product is drowned, is then transferred to a vat, and the liquor is drained off. The product is then washed twice with hot water and then washed with cold water by the displacement method for 30 minutes after which it is drained. The nitrated woodpulp is fed into an 8" Follows and Bates dis-c plate" mill together with sufficient water to give a slurry containing 1 part of nitrocellulose per 61 parts of water. The throughput rate of the mill is 77 lb. (calculated as dry nitrocellulose) per hour. The bulk of the water is drained off and the nitrocellulose, in the form of a slurry 3 containing parts of water per part of nitrocellulose, is fed into a kier where it is heated over a period of 140 minutes up to a temperature of 142 C. at a pressure of 40 lb./sq. in. at which it is held for a further 180 minutes. The kiered product is given two hot water washes followed by two cold water washes after which it is dewatered by centrifuging to give a material having a nitrogen content of 11. 7% (calculated on the dry material), a viscosity of 8 poises (40% solution in 95% acetone) and a water content of 36.4%. This product appears to be identical with and to have the same properties as a nitrocelluloseof the same nitrogen conten and viscosity prepared from cotton linters.

For instance, 10 grams of the product produced as above are dried to a moisture content of 0.5% and added to 100 grams of a lacquer solvent mixture consisting of aliphatic esters 25%, aliphatic. alcohols 20%, aromatic hydrocarbons 55% and the whole gently agitated. The nitrocellulose material completely dissolves in minutes.

10 grams of a sample of similarly dried nitrocellulose of the same nitrogen content and viscosity prepared from cotton linters are added to 100 grams of said lacquer solvent mixture and the whole gently agitated. The nitrocellulose completely dissolves in 17 minutes. p

10 grams of a'- sample of similarly dried nitrocellulose of the same nitrogen content and viscosity prepared from woodpulp in which the milling operation is omitted are added to 100 grams of said lacquer solvent mixture and the whole gently agitated. The nitrocellulosec'omplete ly dissolves in 1-00 minutes.

Example 2 2,400 lb. of woodpulp are diced as in Example 1 and treated with 24,000 lb. of a mixed acid containing 47.59% nitric acid, 38.70% sulphuric acid, 0.02% nitrous acid and 13.69% water for 2 hours. The nitrated product is then drowned and transferred to a vat Where the liquor is dr'ained'ofii afierwhich it is washed with cold water for 30 minutes by displacement and the wash liquor drained off. The washed material so obtained is made into a slurry containing 61 parts water per part nitrocellulose and this slurry is fed into an 8" Follows and Bates disc-plate" mill at a rate of 77 lb. (calculated as dry nitrocellulose) per-hour. The milled slurry is drained and fed into a kier where'it is heated over a period of 2 hours 30 minutes to a temperature of 142 C. and a pressure of 40 lb./sq. in. and is maintained under these conditions for 2 hours 45 minutes after which it is given 30 minutes cutting in a Bertram pulper. The nitrocellulose is then washed once with hot water, and once with cold water and centrifuged. The product so obtained has a nitrogen content of 10.93% (calculated on the dry material), a viscosity of 14 poises (40% solution in 95% acetone) and a water content of 31.9% and appears to be like and to behave similarly to'nitrocellulose of the same nitrogen content and viscosityprepared from cotton linters.

For instance, 4 grams of this product prepared as above are dried and added to amixture of 100 grams of 92% ethanol and 10 grams of camphor and the whole gently agitated. The nitrocellulose completely dissolves in 30 minutes. I

4 grams of a sample of similarly dried nitrocellulose of the same nitrogen content and viscosity prepared from woodpulp in which the'milling operation is omitted are added to 100 grams of the same solventmixture and the whole gently agitated. The nitrocellulose completely dissolves in 90 minutes.

Example 3 2,400 lb. of woodpulp are diced as in Example 1 and treated with 24,000 lb. of a mixed acid containing 50.05% nitric acid, 37.88% sulphuric acid, 0.02% nitrous acid and 12.05% water for 2 hours The reaction mixture is then diluted with suificient water to give a slurry containing 1 part ofnitrocellulose per 54 parts of aqueous liquid and theslurr-y so obtained is fed into an 18" British Rema t disc-platef mil-Lat a rate. 0151288 lb. (calculated as dry nitrocellulose) per hour. The milled slurryis then drained and pumped to a kier where it is heated to a temperatureot 142 C. and apressure of 42 lb./sq. in. over a period of 2 /4 hours and maintained under these conditionsfor' le hours. The kiered product is then cut in a pulper for 30 minutes, washed once with hot water and once with cold water and centrifuged. The nitrocellulose so obtained has a nitrogen content of 11.74% (calculated on the dry material) a viscosity of 9 poises (40% solution in-% acetone) and a water content of 34.2% and has the appearance of and behaves similarly to nitrocellulose of the same nitrogen content and viscosity prepared from cotton linters.

For-instance,- 10 grams of the product produced as above are dried and added to grams of the lacquer solvent mixture referred to in Example 1 and the whole gently agitated. The nitrocellulose completely dissolves in 20 minutes.

10 grams'of a sample of'similarly dried nitrocellulose of the same nitrogen content and viscosity prepared from cotton linters are added to .100 grams of said lacquer solvent mixture and the whole gently agitated. The nifrocelluiose completely dissolves in 18 minutes.

IOgramsof'a sample o'fsimilarly dried nitrocellulose of the same nitrogen content and viscosity prepared from woodpulp in which the. milling operation is omitted are added to 100 grams of said lacquer solvent mixture and the whole gently agitated. The nitrocellulose completely dissolves in 100 minutes.

What I claim is:

1. A process for the production from subdivided sulphite woodpulp sheet of nitrocellulose which dissolves rapidly in solvents therefor and which has the form of nitrated cotton linters which comprises nitrating the pieces of woodpulp sheet, adding water to the resulting nitroceilulose which is in the form of nitrated pieces of woodpulp sheet to produce a slurry thereof, passing said slurry between two opposed and substantially flat surfaces rotating relatively to one another and so spaced from one another as to be, capable of effecting the separation of the fibres of the nitrated pieces of woodpulp sheet without subdividing the said fibres to ,any substantial degree,.and thereafter effecting viscosity reduction and stabilisation of the resulting separated fibres of nitrocellulose.

'2. A process as claimed in claim 1 wherein said aqueous slurry, of nitrated pieces of woodpulp sheet is passed several times between said two opposed surfaces.

3. A processasclaimed in claim 1 wherein said opposed surfaces are the opposed surfaces of plates of a mill.

Referencesfiited. in the file ofthis patent UNITED STATES PATENTS 2,145,862 Collings et al Feb. 7, 1939 2,159,675 Richter May 23, 1939 2,341,221. 1Kingery Feb. 8, 1944 2,652,202 Mallinson et al Sept. 15, 1953 

1. A PROCESS FOR THE PRODUCTION FROM SUBDIVIDED SULPHITE WOODPULP SHEET OF NITROCELLULOSE WHICH DISSOLVES RAPIDLY IN SOLVENTS THEREFOR AND WHICH HAS THE FORM OF NITRATED COTTON LINTERS WHICH COMPRISES NITRATING THE PIECES OF WOODPULP SHEET, ADDING WATER TO THE RESULTING NITROCELLULOSE WHICH IS THE FORM OF NIRATED PIECES OF WOODPULP SHEET TO PRODUCE A SLURRY THEREOF, PASSING SAID SLURRY BETWEEN TWO OPPOSED AND SUBSTANTIALLY FLAT SURFACES ROTATING RELATIVELY TO ONE ANOTHER AND SO SPACED FROM ONE ANOTHER AS TO BE CAPABLE OF EFFECTING THE SEPARATION OF THE FIBRES OF THE NITRATED PIECES OF WOODPULP SHEET WITHOUT SUBDIVIDING THE SAID FIBRES TO ANY SUBSTANTIAL DEGREE, AND THREAFTER EFFECTING VISCOSITY REDUCTION AND STABILISATION OF THE RESULTING SEPARATED FIBERS OF NITROCELLULOSE. 